A common feature of most precious alloys used in watchmaking is their relatively high density (>10 g/cm3). In fact, the two main precious metals used in horology, namely gold and platinum, have respective densities of around 19.3 and 21.5 g/cm3. Consequently, this makes their alloys relatively heavy. Silver and palladium are lighter (10.5 and 12 g/cm3 respectively), but much less used in horology.
Moreover, the use of light metals like titanium and, to a lesser extent, aluminium, in external watch parts, is relatively widespread. However, currently, few alloys can be considered to be both precious (i.e. meet fineness requirements) and light.
WO Patent Application 2012/119647A1 describes ceramic/precious metal compounds able to achieve relatively low densities (<8 g/cm3).
It is not generally possible to obtain ductile metals by creating alloys from light metals and precious metals, and in almost all cases this results in brittle intermediate phases.
However, there is an exception for equiatomic Ti(Pd/Pt/Au) phases. Indeed, these phases may resemble the equiatomic TiNi phase used in some shape memory alloys. Likewise, equiatomic TiPd, TiPt and TiAu phases have some ductility and may, in certain conditions, exhibit behaviour typical of TiNi shape memory alloys. Equiatomic TiPd, TiPt and TiAu alloys have been known for a long time and have been the subject of several studies aimed at high temperature shape memory alloys.
The effect of adding alloying elements other than Ni, Pd, Pt, Au to these systems has mainly been studied for TiNi alloys. Research concerning ternary additions to TiPd, TiPt and TiAu alloys are substantially less common. It is known, however, that adding iron to a TiPd system has an effect on the system's phase transformations.
Most of the literature concerning additions to binary equiatomic alloys of TiNi, TiPd, TiPt and TiAu focuses on modification of the shape memory properties and so-called super-elastic properties of these alloys (amplitude, transition temperature). However, there is no study on the issue of using such alloys in jewelry/horology and the associated constraints, namely shapeability and fineness (percentage of precious metal).
The mass compositions of the ductile equiatomic phases of alloys of TiPd, TiPt and TiAu are shown in Table 1, which sets out the composition of the equiatomic Ti—(Pd, Pt, Au) phases and a comparison to the legal fineness standards applicable in Switzerland.
Legal finenessFineness lowerof preciousthan theAtomicApprox. massmetals inequiatomicAlloycompositioncompositionSwitzerlandcompositionTiPdTi50Pd50Ti310Pd690999, 950, 500500TiPtTi50Pt50Ti197Pt803999, 900, 850—TiAuTi50Au50Ti196Au804999, 750, 585,750, 585, 375375
It is noted that the TiPd and TiAu alloys meet fineness requirements and are therefore of interest for horology and jewelry, as particularly light precious metals.
EP Patent document 0267318 in the name of HAFNER cites certain palladium alloys: 25 to 50% by mass of palladium, with 37 to 69% of silver, and a complement of copper, zinc, gallium, cobalt, indium, tin, iron, aluminium, nickel, germanium, rhenium, but without titanium, and other alloys, from 51 to 95% of palladium, with the addition of different metals, of which only one alloy contains gold, with 70% by mass of palladium, 15% of silver, 5% of copper, 5% of zinc, 3% of platinum, 2% of gold. The only composition disclosed with titanium, of the Ti5Pd95 type, concerns an alloy with 5% titanium, and 95% palladium.
EP Patent document 0239747 in the name of SUMIMOTO describes the addition of 0.001 to 20% of chromium to a titanium-palladium type alloy with 40 to 60 atomic percent of titanium, and the complement of palladium. Seven alloys are disclosed with 50 atomic percent of titanium, with 40 to 50 atomic percent of palladium, and 0 to 10 atomic percent of chromium: Ti50Pd40, Ti50Pd45Cr5, Ti50Pd43Cr7, Ti50Pd42Cr8, Ti50Pd41.5Cr8.5, Ti50Pd41Cr9, Ti50Pd40Cr10.
CH Patent document 704233 in the name of RICHEMONT describes the use in horology of titanium alloys, of the Ti-10-2-3 type including vanadium, iron and aluminium, of the Ti13-11-3 type containing vanadium, chromium and aluminium, of the Ti-15-3 type containing vanadium, chromium, aluminium and tin, of the Ti-5-5-5-3 type containing aluminium, vanadium, molybdenum and chromium. These alloys do not contain either palladium or gold.